The present invention relates to an implant for sealing a defect in the anulus fibrosus of an intervertebral disc, with a retaining portion for insertion into the defect, a sealing element connected to an inner end of the retaining portion and a securing element, connected to the outer end of the retaining portion, which can be fixed to a vertebra adjoining the intervertebral disc, in order to hold the retaining portion in a fixed position, wherein the flexible sealing element has a reduced projected area in a top view from the front along the longitudinal axis of the retaining portion in a first state and has a widened projected area, which is at least twice the reduced projected area, in a second state.
Intervertebral discs consist of two parts: an outer anulus fibrosus (fibrous ring) and an inner nucleus pulposus (jelly-like core). The anulus fibrosus consists of concentric layers of collagen fibres of connective tissue (outer zone), which gradually pass inwardly into fibrous cartilage (inner zone) and surround the nucleus pulposus. The nucleus pulposus is a jelly-like tissue with few cells and with a high water content. It acts in a shock-absorbing manner like a water cushion and absorbs shocks during movement of the spinal column. The intervertebral disc arranged between two vertebrae delimits the distance between the end plates of these vertebrae and, as an elastically deformable damping element, also supports the mobility of the spinal column. The cover plates or end plates, adjoining the intervertebral disc above and below, of the neighbouring vertebrae delimit the so-called intervertebral disc space.
Within the framework of the degeneration of the intervertebral disc that cannot be avoided with increasing age, defects in the form of a tearing or bursting open of the anulus fibrosus often occur. Through such a defect, parts of the nucleus pulposus can escape from the intervertebral disc, which is usually called a herniated disc.
The nucleus pulposus escaping through the defect can, in particular if it escapes dorsally in the direction of the spinal canal of the spinal column, press on neural structures. If this leads to neurological deficits and/or pain, surgery may become necessary. In the event of such surgery, the escaping parts of the nucleus pulposus are removed. However, the defect in the anulus fibrosus is not yet sealed thereby. Specifically, the anulus fibrosus has a hole or a wider or narrower interruption, wherein parts of the jelly-like intervertebral disc core can continue to escape and can lead to discomfort again. Within the framework of a first emergency treatment or for a better introduction of the retaining portion and the sealing element, the defect can also be surgically widened and/or prepared.
In order to durably seal a defect in the anulus fibrosus of an intervertebral disc and to prevent the nucleus pulposus from escaping, the implants defined at the beginning, among other things, are used. The known implant for sealing a defect in the anulus fibrosus of an intervertebral disc, such as is described e.g. in WO 2007/078978 A2, has a retaining portion with a bone anchor which can be fixed to the adjoining vertebra. The retaining portion is inserted into the defect with its inner end and the sealing element secured thereto at the front. The reduced projected area of the sealing element onto a surface perpendicular to the longitudinal axis of the retaining portion allows it to be guided through the defect along this longitudinal axis. The outer end of the retaining portion then terminates more or less flush with the outer side of the anulus fibrosus. The sealing element has the form of a flap, attached to the inner end of the retaining portion, which is to be unfolded after introduction through the anulus fibrosus and is then to seal the entire free defect cross section from the inner side of the anulus fibrosus. The bone anchor is inserted into the intervertebral disc space and is thus anchored in the cover or end plate of an adjoining vertebra in order thus to fix the implant to the vertebra.
The flap of the implant to be laid against the inner wall of the anulus fibrosus according to WO 2007/078978 A2 has to be folded in a first state and has to lie in front of and/or next to the retaining portion in this first state. In the top view from the front along the longitudinal axis of the retaining portion, the sealing element, in the first state, thus has a small cross-sectional area (=projected area onto a plane perpendicular to the longitudinal axis of the retaining portion) and, in this state, can be inserted into the inside of the intervertebral disc through the opening in the anulus fibrosus forming the defect. In a second state, the sealing element is unfolded and rests against the inner side of the anulus fibrosus, wherein it is to cover and seal the defect completely. In this state, the cross-sectional or projected area of the sealing element, seen along the axis of the retaining portion, is typically at least twice as large as in the first state.
The mentioned longitudinal axis of the retaining portion is substantially defined by the direction of insertion of this portion into an opening which is in turn determined by the geometry of the retaining portion and the elements arranged thereon. The longitudinal axis can also be defined as the connection of the outer and inner ends of the retaining portion.
The implant according to WO 2007/078978 A2 above all has the disadvantage that the flap which can theoretically be laid against the inner wall of the anulus fibrosus can be spread out into the desired position only with difficulty or not at all, and that the pressure inside the intervertebral disc displaces this flap and presses it outwards through the defect again.
Furthermore, the intervertebral disc gradually loses volume due to the escape of the nucleus pulposus, but also as a result of aging, and a pressure drop in the intervertebral disc occurs. The height of the intervertebral disc decreases, and thus also the height of the intervertebral disc space. The bone anchor of WO 2007/078978 A2 arranged in the intervertebral disc space can therefore damage the adjoining end plates in the event of an almost inevitable degeneration of the intervertebral disc and cause additional mobility restrictions. The bone anchor durably remaining in the intervertebral disc space can also make interbody fusion at a later time, for example with “cages” (ALIF, TLIF, PLIF, XLIF), more difficult.